Add CLI search and delete commands

[abrookins]

Summary

Adds CLI commands for searching and deleting long-term memories, plus supporting functions.

New CLI Commands

agent-memory search

Search long-term memories with semantic similarity and filters:

agent-memory search "What did we discuss about authentication?"
agent-memory search "project deadlines" --namespace myapp --limit 5
agent-memory search --namespace myapp  # List all memories in namespace
agent-memory search -u user123 --format json

agent-memory delete

Delete memories by ID with confirmation prompts:

agent-memory delete --ids mem1,mem2,mem3
agent-memory delete --ids mem1 --yes  # Skip confirmation
agent-memory delete --ids mem1 --dry-run  # Preview only
agent-memory delete --empty-text  # Delete memories with empty text
agent-memory delete --invalid  # Delete malformed memories

agent-memory delete-session

Delete working memory sessions:

agent-memory delete-session --id session123
agent-memory delete-session --id session123 --namespace myapp

Changes

• cli.py: Added search, delete, and delete-session commands
• long_term_memory.py: Added delete_invalid_memories() and find_memories_with_empty_text() functions
• Full test coverage for new CLI commands and functions

[vishal-bala]

LGTM 👍
(reviewed the CLI changes, but just skimmed the tests)